The present invention pertains to antenna systems for spacecraft and more particularly to a deployable antenna array system which projects a multiple beam pattern with each beam covering a disjoint area.
Spacecraft typically achieve communications (i.e. "uplinks" and "downlinks") with earth-based stations by projecting spot beams to certain areas. These earth-base systems may include but are not limited to land-based stations, water-based stations, such as those located on ships, stations based on airplanes or other spacecraft. The spot beams which are projected by spacecraft may be relatively narrow or broad beams. Small beams are easily focused upon a known earth-based source. For communication situations in which many sources are randomly located over a portion of the earth, that entire portion of the earth must be covered by the antenna system.
For communication by the satellite with a number of earth-based stations, a limited number of communications frequencies or channels exist. Spatial diversity between satellite antenna beams is required. Therefore, satellite communication with a plurality of earth stations is limited to the number of antenna beams (or cells) projected by the antenna system. As cell numbers are increased, spatial diversity becomes difficult to maintain.
In addition, a large number of satellite antennas is difficult to launch into space. Furthermore, large numbers of antennas are difficult to position and deploy in space once the launching vehicle has achieved proper orbit.
Accordingly, it is an object of the present invention to provide uniformly sized spot beams for facilitating communications between satellites and a plurality of earthbased stations.